Genesis of red-bed sandstones in the Minxian region, western Qinling Mountains

The red-bed strata represented by the Upper Cretaceous Mogou Formation in the Xijiang Basin, Minxian are made up of purplish red thick massive conglomerates at the base, followed upwards by red-bed sandstones with tremendous thickness. The genetenic analysis based on depositional sequences, grain sizes and surface features of quartz grains shows that this succession of sandstones has tremendous thickness interbedded with dry channel deposits and thin gravel beds in which the gravels have the features of desert varnish. The sandstones are well sorted, and dominated by medium-grained, fine-grained and very fine-grained sands without clay and silt. The quartz grains are well-rounded, and have well-developed wind scoop, trittkarren, morel basin and siliceous films. All the above-mentioned features suggest that the red-bed sandstones in the study area should be generated from the eolian deposition in the xerothermic conditions.